Initiation of oestrus

ABSTRACT

This invention relates to a method for the initiation of oestrus and ovulation early postpartum, especially but not exclusively, in dairy cows which comprises supplying a prostaglandin post partum and subsequently treating with a progesterone.

This application is a national stage filing under 35 U.S.C. §371 ofPCT/GB00/03423, filed on Sep. 6, 2000, which claims priority to GreatBritain application no. 9921341.5, filed on Sep. 9, 1999. The entirecontents of both of these applications are incorporated by reference.

This invention relates to a process for the inititation of oestrus andovulation early postpartum, especially but not exclusively, in dairycows. The invention also relates to methods of increasing milkproduction.

Reproductive performance is one of the important factors determining theprofitability of dairy herds. Ideally, the calving interval shouldaverage one year, but this can only be achieved if the pregnancy successand detection rate of oestus are high and the interval betweenparturition and first service is less than 90 days (Bulman, D. C. andLamming G. E. J Reprod. Fert (1978) 54: 447-58).

In milked cows, there is a suppression of ovarian follicular developmentfor a variable period after parturition and there is current evidencethat a significant number of animals (about 12%) exhibit prolongedanovulatory periods postpartum (PP) (Royal, M. D., et al., (1999) AnimalScience). In dairy cows there are significant changes in plasma(lutenizing hormone) LH levels after parturition, directly related tothe initiation of ovarian cycles, with low basal LH levels immediatelypostpartum followed by increases in mean levels and the development ofclear LH episodes with increasing episode frequency (Peters A. R. etal., (1981) Journal of Reproduction & Fertility 62: 567-573). There isclear evidence that the low levels of progesterone, secreted as a resultof the initiation of postpartum ovarian follicular development,contribute to establishing a normal oestrous cycle pattern (Lamming, G.E., et al., (1981) Journal of Reproduction and Fertility Supplement 30:155-170). Furthermore, the incidence of the silent ovulation in cyclesprior to insemination delays the intervals to first PP insemination andconception (Senger, P. L. (1994) Journal of Dairy Science 77:2745-2753).

There is a marked interdependence of activity between the ovaries andthe uterus shortly after parturition in mammals such as cows. The earlyresumption of ovarian activity leading to the availability ofcirculating oestradiol—17β, may help to hasten uterine involutionthrough a reduction in size, a marked increase in uterine tone (for areview see Hussein, A. M. (1989) J. Vet Med 36: 641-451) and benefits tothe uterine defence mechanisms (Rowson, L. E. A. et al., (1953)Veterinary Record 65: 335-341). Similarly, the interval to post partum(PP) uterine involution is significantly correlated with the occurrenceof the first PP ovulation (Madej, A. et al., (1984) Theriogenology 21:279-287; Buch, N. C. et al., (1955) Journal of Dairy Science 38: 73-79).An early return to ovarian cyclicity PP was found by most workers to beassociated with high fertility (Thatcher, W. W. and Wilcox, C. J.,(1973) Journal of Dairy Science 56: 608-610; Stevenson, J. S. and Call,E. P. (1983) Theriogenology 19: 367-375; Staples, C. R et al., (990)Journal of Dairy Science 73: 938-947; Senatore, E. M. et al., (1996)Animal Science 62: 17-23; Darwash, A. O. et al., (1997) Animal Science65: 9-16; Kinsel, M. L. and Etherington, W. G. (1998) Theriogenology 50:1221-1238; Mann, G. E. et al., (1998) Nottingham Cattle FertilityConference 11-12. Based on this premise, a number of workers have usedprostaglandin F_(2α). (PGF_(2α)) administration in an attempt to induceearly postpartum uterine recovery or alternatively progesterone (P₄) toinitiate early return to a pattern of normal oestrous cycles, but withinconsistent results. Where a prostaglandin alone has been supplied, ithas been reported that a single dose of PGF_(2α) administered prior today 40 postpartum is beneficial to herd fertility Young, I. M. et al.,(1984) Veterinary Record 115: 429-431; Bernard, M. and Stevenson, J. S.(1986) Journal of Dairy Science 69: 800-811; Young, I. M. and Anderson,D. B. (1986) Veterinary Record 115: 429-431; Etherington, W. G. et al.,(1988) Theriogenology 29: 565-575; MeClary, D. G. et al., (1989)Theriogenology 31: 565-570; White, A. J. and Dobson, H. (1990)Veterinary Record 24: 588-592; Etherington, W. G. et al., (1994)Theriogenology 42: 739-752; Pankowski et al., (1995) Journal of DairyScience 78: 1477-1488, but others have concluded that Here was nosignificant improvement (Mortimer et al., (1984) Theriogenology 21:869-874; Macmillan et al., (1987) Proceeding of the New Zealand Societyof Animal Production 47: 65-68; Stevenson, J. S. and Call, E. P. (1988)Journal of Dairy Science 71; 1926-1933; Armstrong et al., (1989)Veterinary Record 125: 597-600; Morton et al., (1992) AustralianVeterinary Journal 69: 158-160).

Similarly, the administration of P₄ during the PP period is designed toinitiate an early return to normal function of thehypothalamic-pituitary-ovarian axis considered necessary for the earlyinitiation of oestrus, ovulation and luteal activity. However, the useof a progeterone-releasing intra-vaginal device (PRID) on Days 10 to 15PP (Kyle, S. D. (1992) Journal of Dairy Science 75: 1456-1460 or on Days5 to 15 PP (Stevenson, J. S. and Purseley, R. (1994) Journal of DairyScience 77: 726-734) did not include the expected early ovulationcompared with untreated animals. The latter workers reported asignificant increase in the number of treated animals showing overtoestrus at the first PP ovulation compared with untreated controls (64vs 20%).

In an attempt to improve fertility through the induction of a cyclicovarian pattern early PP, a protocol was developed by the inventorsutilising a sequence of PGF₂. and controlled internal drug(progesterone) release (CIDR). Prostaglandin was chosen because of itscleansing effect on the uterine environment (Gustaffson, B. et al.,(1976) Theriogenology 6: 45-50; Etherington, W. G., et al., (1985)Canadian Journal of Comparative Medicine 49: 261-267) and in thepromotion of uterine involution (Lindell, J. O. and Kindhal, H. (1983)Theriogenology 24: 269-274; Bonnet, B. N., et al., (1990) Theriogenology33: 877-890) while a short period (7 days) of progesterone treatmentusing CIDR was designed to stimulate the short luteal phases frequentlyobserved in PP cows (Lamming, G. E., et al., (1981) Journal ofReproduction & Fertility (Supplement) 30: 155-170; Eger, M., et al.,(1988) Animal Reproductive Science 16: 215-224). Furthermore, CIDRinsertion for five days was found to increase the oestrous response tosubsequent PGF_(2α) treatment (Zu, Z. Z., et al., (1997) Theriogenology47: 687-701).

Folman et al., (Anim. Reprod. Sci., 4, 117-26, 1981), discloses a methodof synchronising oestrus in cows, wherein prostaglandin is given latepost partum (after 60 days) followed by progesterone. No indication isgiven suggesting that by giving prostaglandin early post partum followedby progesterone that ovulation and oestrus can be initiated.

Johari et al., (Malay. Agric. Res. Dev. Inst., Res. J., 18, 117-122,1990) discloses a method of synchronising oestrus late post partum(60-90 days) comprising giving progesterone followed by prostaglandin.

The object of the present invention is to initiate ovarian hormonecycles in cows during the early post partum period; previously claimedto be conducive to improved reproductive performance (Stevenson, J. S.and Call, E. P. (1983) Theriogenology 19: 367-375, Darwash, A. O. etal., (1997) Animal Science 65: 9-16).

However, the concept that an early return to PP ovarian cyclicity isconducive to higher fertility has recently been challenged by Smith, M.C. A. and Wallace, J. M. (1998) Reproductive Fertility Development 10:207-216 and their findings, albeit on a limited number of animals, meritscrutiny. These authors showed from milk P₄ analysis of a single herdthat multiparous cows ovulating before 21 days PP exhibited poorerreproductive performance than similar animals ovulating later, an effectnot observed in their primiparous cows. In the multiparous PP cows,there was a high incidence of persistent corpora lutea (PCL), a findingwe have confirmed by study of a wider progesterone database involvingseveral herds, which showed a significant increased incidence of PCL inPP cows between 1975 to 1982 and 1996 to 1998 (Royal, M. D. et al.,(1999) Animal Science (in press). The incidence of PCL during the PPperiod has been associated with a lower submission rate forinsemination, longer intervals to conception, lower pregnancy rates anda higher incidence of embryo loss and therefore, a higher culling rate(Lamming, G. E. and Darwash, A. O. (1998) Animal Reproduction Science52: 175-190). These trends may be influenced by recent changes in thegenetic structure and milk production merit of all UK dairy herds, orassociated with an increased incidence of PP uterine dysfunction. Theideal scenario for maximum fertility is an early return to ovariancyclicity in the PP cow in which the uterus has fully involuted and inthe absence of uterine infection. From knowledge of the influence of apersistent uterine infection on the rate of uterine involution, a cowwith a persistent uterine infection which ovulates by Day 21 postpartummay be expected to experience a delayed luteolysis, therefore a delay inthe return to a normal ovarian cyclic pattern. Thus in herds where thereis an increased incidence of PCL it can be expected that fertilityparameters and pregnancy rates will be adversely affected. The use ofintramuscular (i.m.) injection of PGF_(2α) in methods of the presentinvention is designed to decrease the chances of delayed uterineinvolution and persistent uterine infection.

The inventors have found that a treatment protocol typically using asingle intramuscular injection of PGF_(2α) (Estrumate) on Days 12-14 PPfollowed two days later by progesterone (CIDR) for 7 days was effectivein initiating ovarian cyclicity, reducing the interval to postpartumoestrus and intervals to first insemination and conception (P<0.05). Thetreatment protocol will initiate early ovarian cyclicity, improve heatdetection efficiency, and therefore enhance reproductive performance,particularly in large herds using a block caving management regime.

According to one aspect of the present invention there is provided amethod of initiating oestrus in a female mammal, the method comprisingsupplying a prostaglandin post partum and subsequently treating withprogesterone or a equivalent thereof.

According to another aspect of the invention there is provided a methodof increasing milk production in a female mammal, the method comprisingsupplying a prostaglandin or prostaglandin analogue post partum andsubsequently treating with progesterone or a functional equivalentthereof

There are two distinct aspects of the treatment protocol in methodsaccording to the invention; PGF_(2α) injections to ensure an adequateuterine environment prior to P₄ administration, and P₄ to ensuresensitisation of the hypothalamic-pituitary-ovarian axis, to facilitatefollicle development, ovulation and the manifestation of oestrus. Theprotocol may be applied so that animals would ovulate by Day 25postpartum.

The mammal may be from a domesticated species, particularly a cattlespecies, most preferably a dairy cow.

The prostaglandin may be for example prostaglandin PGF_(2α) or may be asynthetic analogue thereof e.g. dinoprost, cloprostenol, luprostiol,tiaprost, etiproston tromethaline.

The prostaglandin may be supplied on any one of days 12, 13, 14 or 15post partum. The prostaglandin may be supplied by any suitable deliveryroute but is preferably supplied parenterally. The term parenteral, andcognate terms, as used herein includes subcutaneous, intracutaneous,intravenous, intramuscular, intraarticular, intrasynovial, intrasternal,intrathecal, intralesional and intracranial injection or infusiontechniques. Most preferably the prostaglandin is supplied byintra-muscular injection. The prostaglandin is preferably supplied at adose of about 500 μg (or a suitable dose of analogue is supplied to givean equivalent effect).

The term “progesterone” used herein includes natural and syntheticcompounds having relevant biological activity of a naturally occurringprogesterone and includes progesterones isolated or derived from otherspecies. The progesterone or progesterone equivalent may be supplied36-60 hrs, preferably 42-54 hrs most preferably about 48 hrs after thesupply of the prostaglandin.

Preferably, the progesterone is supplied by a controlled internal drugrelease device. The device may be in the form of a plastic intravaginaldevice or may be in the form of or include another controlled/sustainedrelease system such as microcapsules, liposomes, implants, microspheresor the like.

The progesterone or progesterone equivalent may be supplied for 6 to 9days, preferably 7 days. Where the progesterone is supplied by acontrolled internal drug release device, that device may be removedafter 6 to 9 days preferably after 7 days. Where the progesterone issupplied by another controlled/sustained release system that system maybe arranged to stop or reduce the release of progesterone.

The progesterone may be supplied to give a milk progesterone level of 5μg/l.

Preferred progesterone equivalents include:

flugestone acetate

medroxyprogesterone acetate

altrenogest

norgestamet

According to another aspect of the invention there is supplied a kit foruse in initiating oestrus in post partum mammals, or for improving milkproduction in mammals, the kit comprising a prostaglandin or analogueand a progesterone or an equivalent thereof. The prostaglandin may besupplied in a form for parenteral administration—preferablyintramuscular injection. The progesterone or equivalent may be in a formfor controlled internal release. Preferably, the progesterone orequivalent is in a form by which it can be delivered for seven days.

Preferably the kit is arranged to supply a single dose of about 500 μgof the prostaglandin PGF₂ or its equivalent.

The kit is preferably arranged to supply about 1.9 g of a progesteroneor progesterone equivalent over the treatment period.

Methods and kits in accordance with the invention will now be described,by way of example only, with reference to the accompanying drawing,

FIG. 1, which shows the effect of different treatments on levels of milkprogesterone in dairy cows.

1) a Experimental Animals and Milk Sampling

A total of 470 Holstein-Friesian cows with an average parity (number ofpregnancies) of 2.4±0.08, from four farms in the East Midlands wererandomly chosen either to receive hormonal treatment (T, n=155) or toserve as untreated control (C, n=315).

TABLE 1 An audit of experimental animals (n = 470) Control TreatedParity Farm (No.) (No.) (Mean) Calving Pattern A* 92 49 2.38Spring-Autumn B* 98 43 2.27 Spring-Autumn C 60 45 2.78 All Year D 65 181.88 Extended Lactations *Similar breeding and feeding practices.

The cows were housed in a free-stall system and fed rations to meettheir maintenance and production requirements. Data on calving date,parity, insemination date and pregnancy diagnosis were recorded. Milksamples for P4 determinations were taken three times weekly between Day7 to Day 65 postpartum (PP) and on Days 0, 5, and 24 post insemination.All samples were placed in 30 ml plastic bottles, preserved using LactabIII tablets (Thompson and Capper Ltd., Cheshire, England) and stored at4° C. until assayed.

a Hormonal Protocol for the Initiation of Early Cyclicity

The protocol involved a combination of two licensed drugs: a singleinjection i.m. of a luteolytic agent prostaglandin F_(2α) (PGF_(2α)) onDays 12 to 14 PP, followed 48 hours later by an intra vaginal insertionof a progesterone releasing device remaining in situ for seven days. Asynthetic PGF_(2α) was used (2 ml of Estrumate™ containing 500 μg ofCloprostenol, Malinkrodt Veterinary Ltd., Breakspear Road South,Harefield, Uxbridge, Middlesex UB9 6LS) and the source of progesteronewas CIDR (1.9 g progesterone, InterAg, Hamilton, New Zealand).

b Oestrus Detection

In addition to the routine visual checks for oestrous behaviour, allcows were fitted with KAMAR® HEATMOUNT™ detectors (KAMAR, inc., Box773838, Steamboat Springs, Colo. 80477, USA) which were replaced whenthe colour changed to red, usually as a result of the cow having beenmounted indicating standing heat had occurred.

c Milk Progesterone Assay

Milk P₄ concentrations were measured in an un-extacted aliquot of wholemilk by research staff using an enzyme linked immunosorbent assay(ELISA) kit (Ridgeway Science Ltd., Gloucestershire, UK) as reported byDarwash, A. O. et al., (1999) Animal Science. All samples and qualitycontrols (QC) were assayed in duplicate and the mean value of bothreadings was used to indicate milk P₄ concentrations. Eased on QC valuesof 2 and 8 μg/l, the intra-and inter-assay coefficients of variation(CV) were respectively, 9.4 and 10.4% with lower and upper assaysensitivity of <1 to 23.5 μg/l. Furthermore, a routine laboratoryprocedure was adopted whereby all duplicate samples with milk P₄ valuesfrom 1.5 to 10.5 μg/l were re-assayed until the CV of the duplicate was<15%.

Statistical analysis was carried out using GLM procedure of Genstat 5.0for Windows (Rothmstead, Berkshire, UK). Independent effects includedherd, season and parity. Dependent measurements included intervals to PPcommencement of oestrus, luteal activity, the incidence of silentovulation (Days 21-65 PP), days to first PP service and days toconception. Threshold traits were analysed assuming binomial errors.

1. a The Response to Treatment

The responses to treatment were distinguished into categories usingcriteria defined in Table 2 and as demonstrated in FIG. 1.

TABLE 2 Frequency and type of response to hormonal treatment inpostpartum Holstein-Friesian cows (n = 153) Number (%) Type of responseFrequency ovulating No measurable response¹ 12  5 (41.67) Weak response²12  6 (50.00) Hormonal response³ 70 58 (82.86) Physiological response⁴18 17 (94.44) Hormonal and Physiological 41 41 (100.0) ¹Milk P₄ < 2 μg/lduring CIDR treatment, not followed by oestrus. ²Milk P₂ = 2 to <3 μg/lduring treatment not followed by oestrus. ³Milk P₄ > 3 μg/l during CIDRtreatment not followed by oestrus. ⁴Milk P₄ < 3 μg/l during CIDRtreatment followed by oestrus.

There were 24 (15.69%) animals which showed a weak or no-response to theinsertion of CIDR while the remaining 129 (84.31%) showed either ahormonal change (increase in milk P₄ concentration), or a physiologicalresponse (oestus) or both responses following CIDR removal. Theovulation rate immediately following CIDR removal was significantlycorrelated (P<0.01) with the type of response to treatment. Theovulation rate following CIDR removal was 89.22% in 129 animalsclassified as having an adequate response to treatment with the highestovulation rate (100%) occurring in animals showing measurable increasesin milk P₄ levels, followed by behavioural oestrus.

TABLE 3 Effects of treatment on reproductive parameters in postpartumcows (n = 470) % silent Days to PP % in oestrus ovulation Group Days toCLA¹ Oestrus by Day 30 day 21-65 Treated 22.09 ± 0.70^(a) 44.91 ±1.44^(a) 36.77^(a) 42.27^(a) (n = 153) (n = 150) (n = 155) (N = 115)Control 29.62 ± 0.82^(c) 55.62 ± 1.58^(c) 17.72^(c) 56.28^(c) (N = 315)(n = 313) (n = 315) (n = 309) ^(a,c)differ (P < 0.001) ¹CLA =commencement of luteal activity.

As tabulated in Table 3, in addition to shortening the interval to PPcommencement of luteal activity, the treatment significantly shortenedthe interval to PP oestrus, increased the number of animals in oestrusand ovulating by Days 30 and decreased the number of silent ovulationsbetween days 21 to 65 PP, all at P<0.001. The precision of oestrusdetection was enhanced by using KAMAR® heat mount detectors in additionto progesterone monitoring and the herdsman's routine observations.

The effects of herd, seasons and parity on the response to treatment isshown in Table 4.

TABLE 4 Significance levels of the effects on reproductive parametersincluded in the statistical analysis model Reproductive ParametersEffects A B C D E F Herd (H) *** *** * *** Season (S) * Parity (P) ****** *** * Treatment (T) *** ** ** * HXS * HXP * *** SXP * ** HXT SXT *PXT ** * * HXSXP HXSXT HXPXT SXPXT HXSXPXT A = Days to PP commencementof luteal activity (as defined by a level of milk progestrone > 3 μg/ml)B = Days to PP oestrus C = Incidence (%) of silent ovulation on Days21-65 PP D = Days PP to 1st PP service E = Days to PP conception F =Number of services per conception *P < 0.05. **P < 0.001 ***P < 0.001

Although there was no significant effects of herd or parity on theinterval to CLA (Parameter A), there were significant herd and parityeffects on the interval to PP oestrus (Parameter B), interval to PPservice (Parameter D) and days to conception (Parameter E).

Treatment was effective (P<0.001) in reducing the mean interval topostpartum commencement of luteal activity from 29.62±0.82 d to22.09±0.70 d. The mean interval to first PP oestrus in the (Treated) Tanimals was significantly reduced (p<0.001) from 55.62±1.58 d to44.91±1.44 d and the incidence of silent ovulation in cycles betweenDays 21 to 65 PP was reduced (P<0.001) from 56.28% to 42.27%. In twoherds under one management and with a similar block-calving pattern(n=282 animals), the treatment protocol was beneficial to the overallreproductive performance as there was a significant shortening in themean interval to first PP service (75.82±1.93 vs 80.86a±1.32d) and inthe interval to PP conception (83.07±2.49d vs 88.90±1.95), both P<0.05.

The fertility parameters for herds C and D (Table 1) were prejudiced bythe management approach to breeding policy which made it impossible toassess the effects of treatment on the reproductive performance of cowsin these herds. Consequently, analysis of the effects of treatment onfertility was limited to cows in herds A and B; as they were on the sameestate, with comparable parities and managed by a single managementsystem. As shown in Table 5, the treatment protocol has significantly(P<0.05) shortened the interval to PP service and conception withoutaffecting the number of services per conception

TABLE 5 The efficacy of hormonal treatment in the initiation of cyclidtyand subsequent fertility in postpartum (PP) cows in Herds A and B.Services Days to Days to Days to Days to per Group PP CLA PP oestrus PPservice conception conception Treated 20.87 ± 35.90 ± 75.82 ± 83.07 ±1.32 ± (n = 90) 0.86^(a) 1.70^(a) 1.93^(a) 2.49^(a) 0.07^(NS) Control30.08 ± 51.67 ± 80.86 ± 88.90 ± 1.29 ± (190) 1.09^(b) 1.81^(c) 1.32^(b)1.95^(b) 0.05^(NS) ^(a,b)P < 0.05 ^(a,c)P < 0.001, CLA = Commencement ofLuteal activity.

In summary, Eight percent of animals (Table 2) showed no increase inmilk P₄ concentrations during treatment. The remaining animals (92%)showed an increased milk P₄ concentration during CIDR treatment and alsoa clear response within one week of CIDR removal; either a physiologicalresponse by manifestation of oestrus or a hormonal response as shown bythe increased concentrations of milk progesterone (P₄ 3 μg/l) indicatingthat ovulation had occurred (see FIG. 1). There was a considerablevariation among the cows in milk P₄ concentrations during CIDR treatmentas previously demonstrated in ovariectomised cows by Van Cleeff, J. etal., (1992) Animal Reproduction Science 27: 91-106 and considered theresult of variation in metabolism of progesterone absorbed from theCIDR.

The method of the invention successfully decreased the interval topostpartum commencement of luteal activity and as a result it decreasedthe number of days to PP oestrus. It increased the incidence of overtoestrus at both the subsequent and later ovulations up to Day 65 PP alsoobserved by Stevenson, J. S. and Pursely, R. (1994) Journal of DairyScience 77: 725-734. The work of the inventors confirms thatprogesterone is important in regulating hypothalamic-pituitary-ovarianactivity, thus predisposing the treated postpartum animals more likelyto exhibit behavioral oestrus prior to ovulation. There is a generalconsensus that oestradiol arising from follicular maturation is moreeffective in inducing oestrus when progesterone has pre-sensitised thebrain to its action. It also acts on the hypothalamic pituitary axis toincrease the synchrony between pulses of LH an FSH to induce fullovarian cyclicity (Williams, G. L. et al., (1983) Biology ofReproduction 29: 362-373; Stevenson, J. S. and Pursely, R. (1994)Journal of Dairy Science 77: 725-734). Table 4 shows the significance ofthe effects of herd and parity On the various parameters studied

In studying the direct effects of treatment of fertility parameters, theanalysis was confined to pooled data from two herds (A and B); both onone estate, under the same management and feeding regimes and using ablock calving pattern. The management objective was to concentrate thecalving pattern during the spring and autumn. The treatment in theseherds improved overall reproductive performance compared to controls,significantly decreasing the days to PP service and days to conceptionwithout influencing the number of services per conception (see Table 5).The early cyclic ovarian pattern and higher incidence of overt oestrusinduced by the treatment protocol helped to increase the percentage ofanimals inseminated during the first three weeks of the breeding periodand reduced the need of veterinary intervention (Dally, A. E. H. (1997)Cattle Practice 5: 371. Thus the initiation of early ovarian cyclicityin these two herds resulted in an improved reproductive performancewhich is in agreement with that reported by Stevenson, J. S. and Call,E. P. (1983) Theriogenology, 19: 367-375; Darwash, A. O. et al., (1997)Animal Science 65: 9-16 in dairy cows and the findings of Mann, G. E. etal., (1998) Nottingham Cattle Fertility Conference 11-12 in beef cows.

What is claimed is:
 1. A method of initiating oestrus in a femalemammal, the method comprising supplying a prostaglandin or prostaglandinanalogue early post partum and subsequently treating with a progesteroneor progesterone equivalent.
 2. A method of increasing milk production ina female mammal, the method comprising supplying a prostaglandin orprostaglandin analogue post partum and subsequently treating with aprogesterone or progesterone equivalent.
 3. A method according to claim1 in which the mammal is from a domesticated species.
 4. A methodaccording to claim 3 in which the mammal is from a cattle species.
 5. Amethod according to claim 4 in which the mammal is a dairy cow.
 6. Amethod according to claim 1 in which the prostaglandin is prostaglandinPGF_(2α).
 7. A method according to claim 1 in which the prostaglandin orprostaglandin analogue is supplied on one or more of days 12, 13, 14 or15 postpartum.
 8. A method according to claim 1 in which theprostaglandin or prostaglandin analogue is supplied by parenteraladministration.
 9. A method according to claim 8 in which theprostaglandin or prostaglandin analogue is supplied by intramuscularinjection.
 10. A method according to claim 1 in which the prostaglandinor prostaglandin analogue is supplied at a dose of about 500 μg.
 11. Amethod according to claim 1 in which the progesterone or progesteroneequivalent is supplied from about 36 to 60 hours after the supply of theprostaglandin or prostaglandin analogue.
 12. A method according to claim11 in which the progesterone or progesterone equivalent is supplied fromabout 42 to 54 hours after the supply of the prostaglandin orprostaglandin analogue.
 13. A method according to claim 12 in which theprogesterone or progesterone equivalent is supplied from about 48 hoursafter the supply of the prostaglandin or prostaglandin analogue.
 14. Amethod according to claim 1 in which the progesterone or progesteroneequivalent is supplied by a controlled internal drug release device. 15.A method according to claim 1 in which the progesterone or progesteroneequivalent is supplied for about 6 to 9 days.
 16. A method according toclaim 15 in which the progesterone or progesterone equivalent issupplied for 7 days.
 17. A method according to claim 14 in which thecontrolled internal drug release device is removed after 6 to 9 days.18. A method according to claim 17 in which the controlled internal drugrelease device is removed after about 7 days.
 19. A method according toclaim 1 in which the progesterone or progesterone equivalent is suppliedto give a milk progesterone level in the mammal of about 5 μg/l.
 20. Amethod according to claim 1 in which the mammal ovulates by about day 25postpartum.
 21. A kit for use in initiating oestrus in a post partummammal or for increasing milk products in a mammal comprising aprostaglandin or prostaglandin analogue for initial supply to the mammaland a progesterone or progesterone equivalent for subsequent supply tothe mammal, wherein the prostaglandin or prostaglandin analogue is to bedelivered early post partum.
 22. A kit according to claim 21 in whichthe prostaglandin or prostaglandin analogue is in a form which issuitable for parenteral administration.
 23. A kit according to claim 22in which the prostaglandin or prostaglandin analogue is forintramuscular injection.
 24. A kit according to claim 21 in which theprogesterone or progesterone equivalent is in a form for controlledinternal release.
 25. A kit according to claim 24 in which thecontrolled internal release form causes progesterone or progesteroneequivalent to be delivered for 6 to 9 days.
 26. A kit according to claim25 in which the controlled internal release form causes progesterone orprogesterone equivalent to be delivered for about 7 days.
 27. A kitaccording to claim 21 arranged to supply a single dose of about 500 μgof the prostaglandin or prostaglandin.
 28. A kit according to claim 21containing about 1.9 g of a progesterone or progesterone equivalent. 29.A method according to claim 1 in which the prostaglandin analogue iscloprostenol, dinoprost, tiaprost, luprostiol, or etiprostontromethamine.
 30. A method according to claim 1 in which theprogesterone equivalent is flugestone acetate, medroxyprogesteroneacetate, altrenogest, or norgestamet.
 31. A kit according to claim 21 inwhich the prostaglandin analogue is cloprostenol, dinoprost, tiaprost,luprostiol, or etiproston tromethamine.
 32. A kit according to claim 21in which the progesterone equivalent is flugestone acetate,medroxyprogesterone acetate, altrenogest, or norgestamet.